1. Field of the Invention
The present invention relates to a speaker device having an excitation-type structure in which sound is generated by transferring vibration corresponding to an audio signal generated by an actuator such as a giant magnetostrictive actuator to an acoustic diaphragm.
2. Description of the Related Art
A speaker device in which sound is generated by adding vibration to an acoustic diaphragm made of acrylic and the like by an actuator such as a giant magnetostrictive actuator has been invented and has been in practical use, instead of a normal speaker unit having a voice coil and a cone.
Specifically, in JP-A-2007-166027 (Patent Document 1), there is disclosed a device in which a cylindrical acoustic diaphragm is vertically supported, plural magnetostrictive actuators are arranged at a lower end side of the acoustic diaphragm and drive rods of respective magnetostrictive actuators are allowed to abut on a lower end surface of the acoustic diaphragm to add vibration in the axial direction to the acoustic diaphragm.
In the above speaker device, first, the end surface of the cylindrical diaphragm is excited, thereby allowing a compression wave in the longitudinal direction of the cylinder at once. In a process in which the compression wave propagates, force is generated in the radial direction of the cylinder (direction orthogonal to the longitudinal direction of the cylinder) by Poisson's ratio included in a solid. The vibration occurs in the radial direction by the force, as a result, sound waves are generated from the entire cylindrical diaphragm.
Here, Poisson's ratio means the radio between expansion or contract in the direction of force generated when an elastic body is expanded or contracted and expansion or contract in the vertical direction which is the direction orthogonal to the direction of force.
In the speaker device, sound waves are radiated at any position in the axial direction of the acoustic diaphragm in a uniform level and a uniform sound image is formed all over the height (longitudinal) direction of the acoustic diaphragm. That is, a high quality reproduced sound field can be realized.